Throughout the mechanical arts, there is an ever increasing want, need and use of devices that sense and/or read torsional forces applied or directed onto and through elements and parts of mechanisms and that are used to control, record or otherwise manage the application and/or use of such forces.
One widely used form of torque sensing device consists of an elongate torsion member in the form of a rod or bar established of a metal alloy having a predetermined modulous of elasticity and other desired physical properties and/or characteristics. One end of the torsion member is fixed to a mounting plate that can be advantageously secured or anchored in fixed position with said member projecting freely therefrom. One end of the torsion member is fixed to the mounting plate, as by welding, while its other or free end is made to receive those torsional forces to be measured and, most often, is in the form of a polygonal tool engaging head that can be cooperatively engaged by a common wrench socket or the like. The torsion member has one or a plurality of strain gauges fixed to the exterior surface of a central working portion thereof. The strain gauge or gauges are suitably connected with a bridge circuit that is a part of an electric circuit that includes a suitable force indicating read-out device. When torsional forces are directed onto and through the torsion member, the central working portion thereof is torsionally deflected to an extent corresponding to the magnitude of the force applied, the strain gauge or gauges are deflected or biased a corresponding extent and the electrical circuit functions to indicate the magnitude of the applied force, at its read-out device.
The above-noted kind of torque sensing device is that kind of device with which the present invention is concerned and is that kind of device that is commonly referred to and that will here and after be called a Torque Transducer.
The effectiveness, accuracy and dependability of those torque transducers provided by the prior art is often satisfactory in those circumstances where substantial or great torsional forces are to be measured and where the torsion members are made so heavy and stable that they are not subject to be adversely bent or laterally deflected by secondary or random lateral forces that are often directed onto the input ends of the torsion members during ordinary use thereof.
When torque transducers of the character here concerned with are made to receive and measure light or weak torsional forces the central working portions of the torsion members thereof (with which the strain gauges are related) must be made sufficiently small and weak in effective cross-section so that they will torsionally deflect a desired extent when subjected to those light or weak forces sought to be measured.
When the central portions of such devices are made sufficiently weak and small in cross-section to effectively measure light torsional forces, they are often made so weak that they are highly subject to being adversely bent or deflected laterally by small random lateral forces inadvertently applied to the input ends of the members and are thereby rendered undependable and unreliable to give accurate readings.
To overcome the adverse effects of lateral bending or deflection of the working portions of the torque members of torque transducers, the prior art has sought to prevent lateral displacement of the outer or free end portions of the torque members that occur between the central working portions thereof and the heads or work input ends thereof by means of anti-friction bearing means. While use of such bearing means works to prevent great lateral displacement of the bearing-related portions of the torsion members, it has been clearly determined that the necessary working clearances in such bearing means is often or shortly becomes sufficient to allow enough lateral displacement of the torsion members to adversely affect the operation and accuracy of the torque transducers.
In efforts to overcome the above-noted adverse effects of lateral deflection of the torsion members in torque transducers, some in the prior art have lengthened the bearing supported portions of the torsion members and have resorted to the use of two or more axially spaced anti-friction bearings in an effort to afford the members with greater axially stability. While such efforts might notably reduce and in some instances eliminate the adverse effects sought to be overcome, they require the torque transducer to be made notably larger, heavier and far more costly to make.
There are those in the prior art that have sought to reduce the torsional strength of the central working portions of the torsion members of torque transducers without materially reducing the lateral stability or bending strength thereof by making them in the form of cage-like structures, the effective radial or cross-sectional extent and resulting lateral stability of which is not appreciably reduced while sufficient stock is removed therefrom to notably reduce the torsional strength thereof. Such structures are complicated and extremely costly to make and most often fail to afford suitable surfaces to which strain gauges can be easily and effectively fixed.
By far, the most effective, efficient and economical manner in which to reduce and weaken the central working portions of the torsion members of torque transducers is to machine flats at diametrically opposite sides of the central portions of the members so as to present large flat surfaces upon which strain gauges can be easily and conveniently fixed and that result in a central working portion that is substantially rectangular in cross-section. The principal shortcoming of such structures resides in the fact that while they are quite strong and resist lateral bending or deflection through their radial planes that are parallel with the flat surfaces thereof, they are often extremely weak and highly subject to lateral bending and/or deflection through their radial planes that are at right angles or normal to the planes of their flat surfaces.